Immunity To Infectious Diseases

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Immunity To Infectious Diseases

• March 1, 2001

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Infectious Diseases some numbers

• Infectious diseases are the 1 cause of death in
  the Third World
• 1 billion people world-wide are infected with
  some pathogen
• 20 million deaths per year can be attributed to
  infectious diseases
• Less than 5 of research funds are spent each
  year on infectious diseases prevalent in
  Third-World countries

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Infectious Pathogens

• Viruses Obligate intracellular parasites which
  consist of nucleic acid (DNA or RNA) surrounded
  by protein capsid. Viral diseases include common
  cold, flu, measles, mumps, chicken pox, herpes,
  AIDS, polio and rabies.
• Bacteria Prokaryotic microorganisms (mostly
  unicellular) which can cause disease by
  uncontrolled replication and toxin production.
  Bacterial diseases include tuberculosis (1
  infectious killer, worldwide), Lyme disease,
  meningitis, Cholera, ulcers and many types of
  dysentery.
• Protozoa Single-celled animals which can either
  be free-living or parasitic. Diseases caused by
  protozoa include malaria, african sleeping
  sickness, and leishmaniasis.
• Helminths Parasitic worms (flukes, tapeworms,
  nematodes). Diseases caused by helminths include
  schistosomiasis, ascaris infection.

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Evasion of Host Defense Mechanisms by Viruses

• Viral prevention of IFN-a/IFN-b activity (e.g.
  hepatitis C virus)
• Viral inhibition of antigen presentation (e.g.
  herpes simplex viruses, adenoviruses,
  cyto-megaloviruses)
• Viral interference with the complement system
  (e.g. vaccinia viruses)
• Antigenic variation (e.g. influenza, HIV)
• Immunosuppression (e.g. Epstein-Barr virus, CMV,
  HIV, measles, paramyxoviruses)

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Bacterial Infections
- Extracellular infections
- Intracellular infections
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Protozoan Diseases

• Protozoans are single-celled animals which can
  either be free-living or parasitic.
• They typically have quite complex life cycles.
• Diseases caused by protozoa include malaria,
  african sleeping sickness, and leishmaniasis.
• Cytokines and Th1/Th2 balance play an important
  roll in course of disease.

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Helminths

• Helminths are parasitic worms (flukes, tapeworms,
  nematodes).
• Diseases caused by helminths include
  schistosomiasis, ascaris infection, trichinosis.
• Although these organisms are extracellular, they
  generally dont multiply in human hosts and
  therefore do not accumulate in large numbers.
• Consequently, the immune response can be quite
  weak.
• Responses can be both humoral and cellular.

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